1. Field of the Invention
The present application relates to a Gaseous Damping System and method of controlling gaseous fuel flows for a compressed natural gas injector during opening of the injector.
2. Description of the Related Art
Compressed natural gas (hereinafter sometimes referred to as "CNG") is becoming a common automotive fuel for commercial fleet vehicles and residential customers. In vehicles, the CNG is delivered to the engine in precise amounts through fuel injectors, hereinafter referred to as "CNG injectors", or simply "injectors". The CNG injector is required to deliver a precise amount of fuel per injection pulse and maintain this accuracy over the life of the injector. In order to maintain this level of performance for a CNG injector, certain strategies and sequences of operation are required to optimize the combustion of the fuel.
The CNG (Compressed Natural Gas) injector is required to open and close very quickly to promote efficient fuel consumption. In order to accomplish this objective effectively the magnetic circuit utilized to open the valve needle must produce a magnetic field--or flux--relatively quickly across the working gap between the fuel inlet connector and the armature. The CNG injector has a magnetic circuit consisting of an inlet connector, armature, valve body shell, housing and a coil. When energized, the coil produces a magnetic field which is conducted through the magnetic circuit. The flux is conducted through the components and creates an attractive force at the working gap, which force causes upward movement of the armature, with consequent upward movement of the valve needle to open the injector valve.
The CNG injector is required to open and close very quickly. This quick opening creates a relatively severe impact between the armature and the inlet connector. In the CNG injector, the factors which effect impact velocity between the armature and inlet connector are more severe then in a gasoline injector. Compared to a gasoline injector, the CNG injector has two to three times the lift, less spring preload and similar force required to open the injector. The difference is then exaggerated by the lower viscosity (CNG) fluid then gasoline.
A CNG injector requires a much higher flow rate and area to obtain the same amount of energy flow through the injector in a given pulse. This is caused by the lower density of the gaseous CNG when compared to standard gasoline. This requires that the lift for a CNG injector be much greater than it is for a gasoline injector.
The increased lift creates two problems. First, the increased lift substantially reduces the magnetic force available to open the injector. Second, the velocities created because of the longer flight times can be higher, creating higher impact momentum. The reduction in magnetic force also creates another problem. This reduction in force requires the use of a lighter spring preload than in a standard gasoline injector.
A standard gasoline injector usually utilizes about 4 Newton's of spring preload and a very small gasoline force on the needle armature assembly while the injector is closed. In a CNG injector, the force of the gas pressure is about 3 Newton's and the force of the spring is about 2 Newton's. When the CNG injector is energized, the needle armature will begin to move when the magnetic force reaches a level which can overcome the spring and the gas force. The gasoline injector will operate in the same way. However, in a CNG injector, the gas force is removed as soon as the needle/seat seal is broken and the pressure equalizes at the tip of the needle. At this point the magnetic force is substantially higher then it needs to be to lift the armature needle assembly against the force of the spring. This excess magnetic force, combined with a relatively light spring preload, high lift and low viscosity fluid all contribute to high impact velocities between the armature and the inlet connector. We have invented a Compressed Natural Gas Injector which provides gaseous damping for the armature/needle assembly during opening of the gaseous fuel valve.